Surface acoustic wave device and method of manufacture thereof

ABSTRACT

A SAW element ( 13 ) is formed of a piezoelectric substrate ( 14 ), on which are provided IDT electrodes ( 15 ), connection electrodes ( 16 ), underlying metal layers ( 17 ), and acoustic materials ( 18 ) placed on the underlying metal layers ( 17 ) and having surfaces parallel to the main surface of the piezoelectric substrate ( 14 ). The SAW element is mounted in a package ( 10 ), which is provided with external terminals ( 11 ) connected with the connection electrodes ( 16 ), and the package is hermetically scaled with a lid ( 20 ) to form a SAW device. When such a SAW element ( 13 ) is mounted faceup in a package ( 10 ) using a vacuum chuck ( 30 ), its piezoelectric substrate ( 14 ) can be protected against damage. When a SAW element ( 13 ) provided with bumps ( 23 ) on its connection electrodes ( 16 ) is mounted facedown in a package ( 10 ), the failure of electrical connections can be prevented.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a surface acoustic wave devicefor use in wireless communications equipment and the like and method ofmanufacture thereof.

BACKGROUND OF THE TECHNOLOGY

[0002]FIG. 23 is a cross-sectional view of a conventional surfaceacoustic wave device (hereinafter SAW device). Referring to FIG. 23, adescription will be given below on the method of manufacture of theconventional SAW device.

[0003] First, interdigital transducer electrodes (IDT electrodes) 101and connection electrodes 102 are formed by forming vacuum depositedaluminum film on a disk (wafer) of piezoelectric material followed byexposing with a pattern of predetermined configuration and developing.Subsequently, acoustic absorbers 103 are formed by coating a siliconeresin on both sides of the IDT electrodes 101 by screen printing andheat treatment. In this way, a number of surface acoustic wave elements105 (SAW elements) are collectively formed on the wafer. Subsequently,the wafer is diced into individual SAW elements 105.

[0004] Next, a SAW element 105 is secured with adhesive 108 in a package107 having external terminals 106, and the external terminals 106 andconnection electrodes 102 are electrically connected with thin metalwires 109. Subsequently, opening of the package 107 is sealed with a lid110.

[0005] When the acoustic absorbers 103 are formed by screen printing inthis manner, the dimensional accuracy is poor and also their crosssections become dome-like due to drips caused by flow of the resin, thussuffering from the upper surfaces becoming curved and difficulty informing with a uniform height.

[0006] Furthermore, when mounting the SAW element 105 in the package107, as the SAW element 105 is transferred by sucking its surface with avacuum chuck, there is a difficulty in sucking because the top surfacesof the acoustic absorbers 103 are curved and their heights aredifferent. In addition, piezoelectric substrate 100 may incline relativeto the bottom surface of the package 107 thus presenting a possibilityof causing mounting failure.

[0007]FIG. 24 is a cross-sectional view of another conventional SAWdevice. While thin metal wires 109 connect the connection electrodes 102and the external terminals 106 in the conventional SAW device of FIG.23, in another conventional SAW device shown in FIG. 24, projectingelectrodes 111 (bumps) make the connection.

[0008] In this case, too, there is a possibility of causing connectionfailure when the heights of the acoustic absorbers 103 are non-uniformand are greater than the bumps 111.

DISCLOSURE OF THE INVENTION

[0009] The present invention addresses the above issues and aims atproviding a SAW device that can prevent mounting failure when mounting aSAW element in a package.

[0010] In order to attain this object, the SAW device of the presentinvention comprises a package having an external terminal, a SAW elementhoused in the package, and a lid for sealing opening of the package,wherein the SAW element further comprises on the surface of apiezoelectric substrate at least an IDT electrode, a connectionelectrode electrically connected to the IDT electrode, and an acousticabsorber formed on the outside of the IDT electrode, that is, on an endportion of the piezoelectric substrate, in a manner such that its topsurface is parallel to the main surface of the piezoelectric substrate.As the surface of the acoustic absorber is parallel to the main surfaceof the piezoelectric substrate in this way, and as the top surface ofthe acoustic absorber is a plane, it is easy to suck the SAW elementwith a vacuum chuck when mounting in a package and it is possible tosecurely mount it at a predetermined position of the package.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a cross-sectional view of a SAW device in a firstexemplary embodiment of the present invention.

[0012]FIG. 2 is a top view of the SAW device before sealing with a lidin the first exemplary embodiment of the present invention.

[0013]FIG. 3 is a cross-sectional view to illustrate manufacturingprocess of the SAW device in the first exemplary embodiment of thepresent invention.

[0014]FIG. 4 is a top view of a SAW device before sealing with a lid ina second exemplary embodiment of the present invention.

[0015]FIG. 5 is a cross-sectional view of the SAW device in the secondexemplary embodiment of the present invention.

[0016]FIG. 6 is a cross-sectional view of a SAW device in a thirdexemplary embodiment of the present invention.

[0017]FIG. 7 is a top view of the SAW device before sealing with a lidin the third exemplary embodiment of the present invention.

[0018]FIG. 8 is an illustrative diagram of the manufacturing process ofthe SAW device in the third exemplary embodiment of the presentinvention.

[0019]FIG. 9 is a top view of a SAW element in a fourth exemplaryembodiment of the present invention.

[0020]FIG. 10 is a cross-sectional view of a SAW device in the fourthexemplary embodiment of the present invention.

[0021]FIG. 11 is a cross-sectional view of a SAW device in the fourthexemplary embodiment of the present invention.

[0022]FIG. 12 is a top view of a SAW element in a fifth exemplaryembodiment of the present invention.

[0023]FIG. 13 is a cross-sectional view of a SAW device in the fifthexemplary embodiment of the present invention.

[0024]FIG. 14 is a top view of a SAW element in a sixth exemplaryembodiment of the present invention.

[0025]FIG. 15 is a cross-sectional view of a SAW device in the sixthexemplary embodiment of the present invention.

[0026]FIG. 16 is a top view of a SAW element in a seventh exemplaryembodiment of the present invention.

[0027]FIG. 17 is a cross-sectional view of a SAW device in the seventhexemplary embodiment of the present invention.

[0028]FIG. 18 is a cross-sectional view of a SAW device in an eighthexemplary embodiment of the present invention.

[0029]FIG. 19 is a top view of a SAW device before sealing with a lid ina ninth exemplary embodiment of the present invention.

[0030]FIG. 20 is a top view of a SAW device before sealing with a lid ina tenth exemplary embodiment of the present invention.

[0031]FIG. 21 is a top view of a SAW device before sealing with a lid inan eleventh exemplary embodiment of the present invention.

[0032]FIG. 22 is a cross-sectional view of a SAW device in a twelfthexemplary embodiment of the present invention.

[0033]FIG. 23 is a cross-sectional view of a conventional SAW device.

[0034]FIG. 24 is a cross-sectional view of a conventional SAW device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring to drawings, a description will be given below onexemplary embodiments of the SAW device and method of manufacturethereof of the present invention.

[0036] First Exemplary Embodiment:

[0037] Referring to FIGS. 1 to 3, a description will be given on a firstexemplary embodiment of the present invention.

[0038] A uniform thickness vapor deposited film composed of aluminum ora metal having aluminum as the main constituent is formed on the mainsurface of a wafer composed of a piezoelectric material such as quartz,LiTaO₃, LiNbO₃, and the like. Positive type photoresist is thenuniformly coated by spin coating on top of the vapor deposited film.Next, the photoresist is exposed and developed so as to make IDTelectrodes 15 having a desired shape, connection electrodes 16 to beconnected to the IDT electrodes 15, and underlying metal layers 17 to bedisposed at the locations where acoustic absorbers are to be formed, andthen the vapor deposited film is etched to obtain IDT electrodes 15,connection electrodes 16, and underlying metal layers 17, and thephotoresist is removed. Here, the underlying metal layers 17 are formedto a size greater than the acoustic absorbers to be formed.

[0039] Subsequently, the entire main surface of the wafer whereon theIDT electrodes 15 have been formed is covered with a negativephotoresist film, which is then pressed while being heated. The exposedportion of the film resist is to become acoustic absorbers 18 and a filmresist having the same thickness as that of the acoustic absorbers 18are used.

[0040] Subsequently, acoustic absorbers 18 are formed by exposing anddeveloping the portion which will form the acoustic absorbers 18 in amanner such that the film resist of that portion will remain. Afterdevelopment, moisture in the acoustic absorbers 18 is removed so as toimprove adhesion with the piezoelectric substrate 14. When moisture isremaining in the acoustic absorbers 18, there is a possibility ofcausing a change in the quality of the acoustic absorbers 18 orcorrosion of the IDT electrodes 15. A plurality of SAW elements 13 areformed on the wafer in this manner.

[0041] Next, the wafer is cut into individual SAW elements 13 with adicer while spraying with water. After removing moisture, a SAW element13 is transferred by sucking its surface, that is, the surfaces of theacoustic absorbers 18 with a vacuum chuck 30 shown in FIG. 3, and ismounted in a package 10 coated with an adhesive 12. During this process,as the acoustic absorbers 18 have the same thickness and, in addition,as their top surfaces are formed parallel to the surface of thesubstrate 14, the SAW element 13 can be securely sucked with the vacuumchuck 30 and can be accurately mounted in the package 10.

[0042] Next, as illustrated in FIG. 2, the connection electrodes 16 ofthe SAW element 13 and the external terminals 11 of the package 10 areelectrically connected with thin metal wires 19, the opening of thepackage 10 is sealed with a lid 20, and a SAW device shown in FIG. 1 isobtained.

[0043] Second Exemplary Embodiment:

[0044] Referring to FIGS. 4 and 5, a description will be given on asecond exemplary embodiment of the present invention.

[0045] First, a plurality of SAW elements 13 having IDT electrodes 15,connection electrodes 16, and underlying metal layers 17 are formed on awafer in a manner similar to the first exemplary embodiment. Next, acoupling layer 21 is formed by uniformly spin coating a silane-basedunderlying coupling agent over the entire surface on the side of thewafer where the IDT electrodes 15 have been formed. Subsequently,solvent component in the coupling layer 21 is removed by drying.

[0046] Afterwards, as in the first exemplary embodiment, the entire mainsurface of the wafer is covered with a negative photoresist film, whichis then pressed while being heated. As the film resist, one having thesame thickness as the thickness of the acoustic absorbers 18 to beformed is used. Next, that portion of the film resist which will formthe acoustic absorber 18 is exposed and developed. After acousticabsorbers 18 have been formed, moisture in the acoustic absorbers 18 isremoved. Next, after dicing the wafer into individual SAW elements 13 asin the first exemplary embodiment, a SAW element 13 is mounted in apackage 10 and a SAW device as illustrated in FIGS. 4 and 5 is obtained.

[0047] In this exemplary embodiment, too, as in the first exemplaryembodiment, the top surfaces of the acoustic absorbers 18 are formedparallel to the surface of the piezoelectric substrate 14 thus enablingsecure suction of the SAW element 13 with the vacuum chuck 30 shown inFIG. 3 and mounting in the package 10.

[0048] Furthermore, as the silane-based coupling layer 21 formed in thisexemplary embodiment has a large force of adhesion with the acousticabsorbers 18 and the piezoelectric substrate 14, and is extremely thinas it is a monomolecular layer, it enables to greatly enhance theadhesion strength between the acoustic absorbers 18 and thepiezoelectric substrate 14 without affecting the sound absorbing effect.As a result, when dicing the wafer on which a plurality of SAW elements13 have been formed into individual SAW elements 13, peeling off theacoustic absorbers 18 from the piezoelectric substrate 14 due to sprayedwater can be prevented. In addition, acoustic absorbers 18 that arestronger to thermal stress and the like to be experienced while sealingopening of the package 10 with a lid 20 with solder, for example, ormounting a SAW device onto a circuit board by solder reflow method canbe formed.

[0049] In the meantime, although only necessary parts of the couplinglayer 21 are shown in FIGS. 4 and 5 for easy understanding, in thissecond exemplary embodiment, the coupling layer 21 is provided over theentire surface of the piezoelectric substrate 14 covering the IDTelectrodes 15 and the connection electrodes 16.

[0050] Third Exemplary Embodiment:

[0051] Referring to FIGS. 6, 7, and 8, a description will be given on athird exemplary embodiment of the present invention.

[0052] IDT electrodes 15, connection electrodes 16, and underlying metallayers 17 composed of aluminum film or aluminum alloy film are firstformed on a wafer by photolithography in a manner similar to the firstexemplary embodiment. Next, as illustrated in FIG. 8, a wafer 81 onwhich SAW elements 13 have been formed and an electrode 85 made ofstainless steel and the like are immersed in a liquid electrolyte 83,and a voltage is applied or a current is supplied from a power supply 86using the electrode 85 as the cathode and a current supplying wire 87that collects leads 82 form the IDT electrodes 15, connection electrodes16 and the underlying metal layers 17 as the anode. Here, the numeral 84is a chemically resistant vessel. With this treatment, surfaces of theIDT electrodes 15, connection electrodes 16 and the metal layers 17including respective sides are oxidized and are covered with aprotective film 22 as shown in FIG. 6. Then, the wafer 81 is pulled outfrom the liquid electrolyte 83 and cleansed by dipping in pure water.

[0053] Next, the wafer 81 is diced into individual SAW elements 13 afterforming a coupling layer 21 and acoustic absorbers 18 in a mannersimilar to the second exemplary embodiment.

[0054] Next, a SAW element 13 is mounted in a manner similar to thesecond exemplary embodiment in a package 10 coated with an adhesive 12,external terminals 11 and connection electrodes 16 are electricallyconnected with thin metal wires 19 as illustrated in FIG. 7, opening ofthe package 10 is sealed with a lid 20, and a SAW device shown in FIG. 6is obtained.

[0055] In this exemplary embodiment, too, as in the first exemplaryembodiment, the top surfaces of the acoustic absorbers 18 are formedparallel to the main surface of the piezoelectric substrate 14 thusenabling secure suction of the SAW element 13 with the vacuum chuck 30shown in FIG. 3 and mounting in the package 10.

[0056] Furthermore, in this exemplary embodiment, too, the silane-basedcoupling layer 21 can greatly enhance the adhesion strength between theacoustic absorbers 18 and the piezoelectric substrate 14 withoutaffecting the sound absorbing effect. As a result, peeling off theacoustic absorbers 18 from the piezoelectric substrate 14 when dicingthe wafer into individual SAW elements 13 by spraying water can beprevented. In addition, acoustic absorbers 18 that are stronger tothermal stress and the like to be experienced when solder sealing anopening of the package 10 with a lid 20, for example, or mounting a SAWdevice on a circuit board by reflow and other methods can be obtained.

[0057] In this exemplary embodiment, anodic oxidation was carried outafter forming the IDT electrodes 15 and connection electrodes 16. As thedeveloping solution for photosensitive resin is generally alkaline,there is a possibility of the IDT electrodes 15 and connectionelectrodes 16 that consist of aluminum or a metal having aluminum as themain constituent being eroded when developing the film resist that willform the acoustic absorbers 18. However, by covering the surfacesincluding the sides of the IDT electrodes 15 and the connectionelectrodes 16 with a protective film 22 consisting of alkali resistantaluminum oxide as in this exemplary embodiment, each of the electrodescan be protected against adverse effect by the developing solution.

[0058] Also, as the protective film 22 is electrically insulating,short-circuit failure of electrodes can be prevented in the event anelectrically conductive foreign object drops onto the SAW element 13.

[0059] In this exemplary embodiment, anodic oxidation was carried outafter the IDT electrodes 15, connection electrodes 16 and underlyingmetal layers 17 had been formed; however, it does not matter if anodicoxidation of the surface of vapor deposited film having aluminum oraluminum alloy as the main constituent is carried out before forming theIDT electrodes 15, connection electrodes 16, and underlying metal layers17, followed by formation of the IDT electrodes 15, the connectionelectrodes 16, and the underlying metal layers 17 thereby making theirtop surfaces covered with an insulating protective film. In this case,during the period of development for forming the IDT electrodes 15, theconnection electrodes 16, and the underlying metal layers 17, at leastsurfaces of the IDT electrodes 15 and the connection electrodes 16 willnot be eroded by alkaline developing solution. However, as the sides arenot covered with the protective film 22, it is preferable to carry outanodic oxidation after forming the IDT electrodes 15 as in theabove-mentioned exemplary embodiment in order to prevent erosion by thedeveloping solution for forming the acoustic absorbers 18.

[0060] By carrying out anodic oxidation and covering the surface with aprotective film 22 either before or after forming the IDT electrodes 15in this way, an effect of preventing erosion of the IDT electrodes 15and the connection electrodes 16 due to alkaline developing solutionhigher than by not forming a protective film 22 can be obtained.

[0061] Fourth Exemplary Embodiment:

[0062] Referring to FIGS. 9, 10, and 11, a description will be given ona fourth exemplary embodiment of the present invention.

[0063] First, IDT electrodes 15, connection electrodes 16, andunderlying metal layers 17 are formed on a wafer in a manner similar tothe first exemplary embodiment followed by forming acoustic absorbers 18on the underlying metal layers 17. The acoustic absorbers 18 have aheight enough for forming a space necessary for the IDT electrodes 15 toexcite surface acoustic waves (SAW) after being packaged in a package10.

[0064] Next, gold bumps 23 are formed on the connection electrodes 16.The height of the bumps 23 is made higher than that of the acousticabsorbers 18.

[0065] Subsequently, the wafer is diced in the same way as in the firstexemplary embodiment to obtain a SAW element 13 illustrated in FIG. 9.

[0066] The SAW element 13 is then mounted with the side having the bumps23 facedown in the package 10 having external terminals 11, and theconnection electrodes 16 of the SAW element 13 and the externalterminals 11 are electrically connected through the bumps 23.

[0067] During this process, the height of the bumps 23 decreases due toheating and pressing.

[0068] In the case of conventional acoustic absorbers 103 shown in FIG.24, as the height of each of the acoustic absorbers 103 differs and itscross section is domed, in connecting connection electrodes 102 of a SAWelement 105 and external terminals 106 of a package 107 using bumps 111,there is a possibility of not being able to obtain a SAW device havingdesired characteristic since the SAW element 105 cannot be horizontallymounted in the package 107 when the height of bumps 111 has decreased toits minimum.

[0069] However, in this exemplary embodiment, as the heights of theacoustic absorbers 18 are fixed and their top surfaces are parallel tothe piezoelectric substrate 14, in the event the height of bumps 23 haslowered as shown in FIG. 11 during the mounting process, the acousticabsorbers 18 work as stoppers and prevent the bumps 23 from becominglower than the height of the acoustic absorbers 18 thereby enabling tosecure enough space for the IDT electrodes 15 to excite SAW. Also, asthe SAW element 13 can be horizontally mounted, the dispersion ofjoining strength between the bumps 23 and the connection electrodes 16can be reduced. In other words, a SAW element 13 such as this is strongagainst mechanical and thermal stress.

[0070] Thereafter, opening of the package 10 is sealed with a lid 20 toobtain a SAW device as illustrated in FIG. 10.

[0071] While bumps 23 are formed with gold in this exemplary embodiment,they may be formed with solder and the like.

[0072] Fifth Exemplary Embodiment:

[0073] Referring to FIGS. 12 and 13, a description will be given on afifth exemplary embodiment of the present invention.

[0074] First, IDT electrodes 15, connection electrodes 16, underlyingmetal layers 17, and coupling layers 21 are formed on a wafer in amanner similar to the second exemplary embodiment.

[0075] Next, the entire surface of the wafer is covered with a negativephotosensitive film resist and heated, and the film resist is pressed.As the film resist, one having the same thickness as that of theacoustic absorbers 18 to be formed is used. Next, the film resist isexposed and developed in a manner such that the portion of the filmresist forming the acoustic absorbers 18 will remain and the acousticabsorbers 18 are obtained. The acoustic absorbers 18 have a heightenough for the IDT electrodes 15 to form a space necessary for excitingSAW after being mounted in a package 10.

[0076] Next, the wafer is diced into individual SAW elements 13 as shownin FIG. 12 after forming bumps 23 on the connection electrodes 16 in amanner similar to the fourth exemplary embodiment, mounted in a package10, and a SAW device as shown in FIG. 13 is obtained.

[0077] In this exemplary embodiment, too, as in the fourth exemplaryembodiment, as the acoustic absorbers 18 work as stoppers at the timethe SAW element 13 is being mounted, the height of the bumps 23 will notbecome lower than the height of the acoustic absorbers 18 and a spacenecessary for the IDT electrodes 15 to excite SAW can be secured. Also,during this process, as the SAW element 13 can be horizontally mounted,the dispersion of adhesion strength between the bumps 23 and theconnection electrodes 16 can be reduced. In other words, a SAW devicesuch as this is strong against mechanical and thermal stress.

[0078] Furthermore, in this exemplary embodiment, as in the secondexemplary embodiment, by forming a coupling layer 21 between theunderlying metal layers 17 and the acoustic absorbers 18, the adhesionstrength between the acoustic absorbers 18 and the piezoelectricsubstrate 14 can be greatly enhanced without affecting the soundabsorbing effect. As a result, peeling off the acoustic absorbers 18from the piezoelectric substrate 14 by spraying water when dicing thewafer into individual SAW elements 13 can be prevented. In addition,acoustic absorbers 18 that are stronger to stress such as thermal stressto be experienced while solder sealing opening of the package 10 with alid 20, for example, or mounting a SAW device on a circuit board byreflow and other methods can be provided.

[0079] Although only necessary parts of the coupling layer 21 are shownin FIGS. 12 and 13 for ease of understanding, in this exemplaryembodiment the coupling layer 21 is provided over the entire surface ofthe piezoelectric substrate 14 covering the IDT electrodes 15 and theconnection electrodes 16.

[0080] Sixth Exemplary Embodiment:

[0081] Referring to FIGS. 14 and 15, a description will be given on asixth exemplary embodiment of the present invention.

[0082] First, IDT electrodes 15, connection electrodes 16, andunderlying metal layers 17 of which the surfaces and the sides have beencovered with an insulating protective film 22 are formed in a mannersimilar to the third exemplary embodiment.

[0083] Going through the same subsequent processes as in the fourth andfifth exemplary embodiments, acoustic absorbers 18 are formed on theunderlying metal layers 17. After further forming bumps 23 on theconnection electrodes 16, wafer is diced into individual SAW elements 13shown in FIG. 14. Next, a SAW device as shown in FIG. 15 is fabricatedby mounting a SAW element 13 in a package 10 and sealing with a lid 20.

[0084] In this exemplary embodiment, as in the third exemplaryembodiment, since the surfaces and sides of the IDT electrodes 15,connection electrodes 16, and underlying metal layers 17 are coveredwith a protective film 22, erosion of the IDT electrodes 15 and theconnection electrodes 16 by alkaline liquid electrolyte duringdevelopment for the formation of the acoustic absorbers 18 can beprevented.

[0085] Also, as described in the third exemplary embodiment, theelectrically insulating protective film 22 may be formed on the surfacesof the IDT electrodes 15 and the connection electrodes 16 by carryingout anodic oxidation after a metal film of aluminum or aluminum alloyhas been formed on the wafer prior to the formation of the IDTelectrodes 15, connection electrodes 16, and underlying metal layers 17.

[0086] Seventh Exemplary Embodiment:

[0087] Referring to FIGS. 16 and 17, a description will be given on aseventh exemplary embodiment of the present invention. In this exemplaryembodiment, only the difference from the SAW device of the fourthexemplary embodiment will be described.

[0088] In this exemplary embodiment, as shown in FIG. 16, underlyingmetal layers 17 and acoustic absorber 18 to be formed thereon are formedin the shape of a frame on the periphery of a piezoelectric substrate 14in a manner such that they surround IDT electrodes 15 and connectionelectrodes 16. The method of formation is the same as in the fourthexemplary embodiment.

[0089] After a SAW element 13 has been mounted in a package 10, a filler25 composed of a silicone-based resin is filled between the SAW element13 and the inner wall of the package 10 and then cured by heating.During this process, the frame-shaped acoustic absorber 18 prevents thefiller 25 from flowing into the SAW excitation space of the IDTelectrodes 15.

[0090] In addition, the filler 25 has, after being cured, a higherelasticity than the acoustic absorber 18 and can absorb spurious wavesthat have not been absorbed by the acoustic absorber 18 and can alsorelieve the stress applied to the SAW element 13 due to the differencein thermal expansion coefficients between those of the SAW element 13and the package 10 thus preventing change of characteristics.

[0091] Eighth Exemplary Embodiment:

[0092] Referring to FIG. 18, a description will be given on an eighthexemplary embodiment of the present invention.

[0093] The difference of a SAW device of this exemplary embodiment fromthe SAW device of the seventh exemplary embodiment lies in that a filler25 is provided not only between the SAW element 13 and the inner wall ofthe package 10 but also on the rear surface of the SAW element 13 facinga lid 20. Other structure is the same. As a result, a further highereffect of absorbing spurious waves is obtained compared with that of theSAW device of the seventh exemplary embodiment.

[0094] While the filler 25 is provided in this exemplary embodiment overthe entire rear surface of the SAW element 13 facing the lid 20, similareffect of absorbing spurious waves is obtainable by providing only onthe portions corresponding to the IDT electrodes 15.

[0095] Also, when sealing the package 10 with the lid 20, it ispreferable that care be taken not to make the filler 25 provided on therear surface of the SAW element 13 facing the lid 20 and the lid 20 comein contact with each other in order to prevent deterioration of thecharacteristics caused by deformation of the SAW element 13 due to anexcessive pressure applied from the rear surface of the SAW element 13.

[0096] Ninth Exemplary Embodiment:

[0097] Referring to FIG. 19, a description will be given on a ninthexemplary embodiment of the present invention.

[0098] In this exemplary embodiment, as illustrated in FIG. 19, twopairs of IDT electrodes 15 are integrated into one unit, two surfaceacoustic wave units (SAW units) 27 provided with reflector electrodes 26on both sides of them are provided in parallel on a piezoelectricsubstrate 14, and an acoustic absorber 18 is formed on the piezoelectricsubstrate 14 between the SAW units 27 with intervention of an underlyingmetal layer 17. By employing this structure, acoustic coupling betweenthe two SAW units 27 can be suppressed, providing a superior quantity ofout-of-band attenuation.

[0099] As the acoustic absorber 18 is made by the method described inthe first exemplary embodiment and the top surface is parallel to thesurface of the piezoelectric substrate 14, it enables mounting of a SAWelement 13 in a package 10 by securely sucking the SAW element 13 with avacuum chuck 30 shown in FIG. 3.

[0100] In a SAW device having a plurality of SAW units 27 on a singlepiezoelectric substrate 14, it is preferable to provide an acousticabsorber 18 at least between opposing IDT electrodes 15 between the twoSAW units 27 and suppress acoustic coupling. Also, in the SAW units 27,when reflector electrodes 26 are provided between the IDT electrodes 15or at both ends of the IDT electrodes 15, it is preferable to provide anacoustic absorber 18 fabricated by a similar method not only between theIDT electrodes 15 between the SAW units 27 as described above but alsobetween the reflector electrodes 26.

[0101] Tenth Exemplary Embodiment:

[0102] Referring to FIG. 20, a description will be given on a tenthexemplary embodiment of the present invention.

[0103] In this exemplary embodiment, acoustic absorbers 18 are providednot only between two SAW units 27 but also between reflector electrodes26 and the end of a piezoelectric substrate 14 in the direction ofpropagation of SAW as illustrated in FIG. 20. Needless to say, theacoustic absorbers 18 are provided on the piezoelectric substrate 14with intervention of underlying metal layers 17 in a manner similar tothe first exemplary embodiment. As these acoustic absorbers 18 and theacoustic absorber 18 between the SAW units 27 are of the same thicknessand their main surfaces are formed parallel to the surface of thepiezoelectric substrate 14, it enables secure sucking of a SAW element13 with a vacuum chuck shown in FIG. 3 and mounting in a package 10.

[0104] By employing this structure, the effect of absorbing spuriouswaves can be further enhanced compared with the SAW device of the ninthexemplary embodiment.

[0105] Eleventh Exemplary Embodiment:

[0106] Referring to FIG. 21, a description will be given on an eleventhexemplary embodiment of the present invention.

[0107] When trying to minimize the inductance between connectionelectrodes 16 and external terminals 11 by shortening thin metal wires19 connecting the connection electrodes 16 and the external terminals11, a wiring electrode is generally provided from the connectionelectrodes 16 to an end of a piezoelectric substrate 14 which is closeto the external terminals 11 to be connected.

[0108] However, by connecting the connecting electrodes 16 withunderlying metal layers 17, and connecting the external terminals 11 tobe connected with the underlying metal layers 17 using thin metal wires19 as in this exemplary embodiment illustrated in FIG. 21, the thinmetal wires 19 can be shortened without newly providing a wiringelectrode.

[0109] In this way, downsizing of a SAW device can be achieved.

[0110] Here, the SAW device of this exemplary embodiment is fabricatedaccording to the method of manufacture described in the first exemplaryembodiment with the exception that the connection electrodes 16 and theunderlying metal layers 17 are made in a connected state. As acousticabsorbers 18 provided between IDT electrodes 15 and an end of apiezoelectric substrate 14 are of the same thickness as in the firstexemplary embodiment, and the top surfaces of them are formed parallelto the surface of the piezoelectric substrate 14, it enables securesucking of a SAW element 13 with a vacuum chuck shown in FIG. 3 andmounting of it in a package 10.

[0111] Twelfth Exemplary Embodiment:

[0112] Referring to FIG. 22, a description will be given on a twelfthexemplary embodiment of the present invention.

[0113] In this exemplary embodiment, an antireflective film 28 ofamorphous silicon or silicon nitride that absorbs light well is formedover the entire rear surface of a wafer composed of crystal, LiTaO3,LiNbO3, or the like.

[0114] A uniform thickness vapor deposited film consisting of aluminumor a metal having aluminum as the main constituent is formed on the mainsurface of such a wafer. Subsequently, a positive photoresist isuniformly spin coated on the vapor deposited film.

[0115] Next, the photoresist is exposed in a manner such that IDTelectrodes 15 having a desired shape and connection electrodes 16 to beconnected to the IDT electrodes 15 can be formed. In this case, as theantireflective film 28 has been formed on the rear surface of the wafer,it absorbs the light passing the wafer and prevents light fromreflecting on the main surface of the wafer.

[0116] Next, the photoresist is developed to form IDT electrodes 15 andconnection electrodes 16, and an electrically insulating protective film22 is formed by anodic oxidation on the surface of the IDT electrodesand connection electrodes 16 including their sides.

[0117] Subsequently, in the same manner as in the second exemplaryembodiment, coupling layers 21 are formed at least at the location onthe wafer surface where acoustic absorbers 18 are to be formed.

[0118] Next, the entire surface of the wafer on which the IDT electrodes15 have been formed is covered with a negative photosensitive filmresist, which is then pressed while being heated. As the film resist,one having the same thickness as that of the acoustic absorbers 18 to beformed is used.

[0119] Next, the portion of the film resist that will form the acousticabsorbers 18 is exposed. In this case, too, the antireflective film 28on the rear surface of the wafer absorbs light passing through the waferand prevents it from reflecting on the main surface of the wafer.

[0120] Afterwards, development is made to obtain acoustic absorbers 18.After development, moisture in the acoustic absorbers 18 is removed toimprove adhesion with a piezoelectric substrate 14.

[0121] Thereafter, a SAW device shown in FIG. 22 is fabricated in thesame manner as in the first exemplary embodiment.

[0122] In this SAW device, as the acoustic absorbers 18 on both sides ofthe IDT electrodes 15 have the same thickness as in the first exemplaryembodiment and are formed in a manner such that their top surfaces areparallel to the surface of the piezoelectric substrate 14, it enablessecure sucking of a SAW element 13 with a vacuum chuck 30 shown in FIG.3 and mounting of it in a package 10.

[0123] In the meantime, although the antireflective film 28 is formed inthis exemplary embodiment before a vapor deposited metal film is formed,acoustic absorbers 18 having superior configurational accuracy can beobtained by forming the antireflective film 28 before exposing the filmresist that will form the acoustic absorbers 18. However, the IDTelectrodes 15 and the connection electrodes 16 can be formed with higheraccuracy when the antireflective film 28 is formed before forming theIDT electrodes 15.

[0124] Also, although the antireflective film 28 is formed over theentire rear surface of the wafer, it is preferable to form it largerthan at least the portions that will form the acoustic absorbers 18, IDTelectrodes 15, and connection electrodes 16 so that transmitting lightthat reflects on the rear surface of the wafer will not impinge on thephotosensitive resin that will form the acoustic absorbers 18 and theIDT electrodes 15 and the photosensitive resin that will form theconnection electrodes 16.

[0125] A description of the gist of the present invention will be givenin the following.

[0126] (1) In each of the above-mentioned exemplary embodiments, theacoustic absorbers 18 are formed using a film type negativephotosensitive resin in order that they can be stably fabricated with ahigher sound absorbing effect, smaller area, and lower profile. However,similar effect is obtainable by coating on a wafer a photosensitiveresin solution by spin coating and the like to a uniform thickness. Atthis time, as the thickness achievable by a single spin coating issmall, spin coating of the photosensitive resin solution may be repeatedseveral times to adjust to a desired thickness of the acoustic absorbers18.

[0127] (2) In each of the above-mentioned exemplary embodiments, theacoustic absorbers 18 are formed using a photosensitive resin selectedfrom the group consisting of epoxy resin, acrylic resin, and polyimideresin that are resilient and can efficiently absorb spurious waves. Inparticular, acrylic resin is preferable because of its superior adhesionto a piezoelectric substrate 14.

[0128] (3) While the acoustic absorbers 18 may be formed in a nearlysquare shape, it is preferable to form them in a manner such that theend portions of the acoustic absorbers 18 on the side of the IDTelectrodes 15 are saw-toothed as shown in each of the above exemplaryembodiments so that scattering effect can be obtained in addition tosound absorbing effect, thereby enhancing suppression of spurious waves.Also, peeling off the acoustic absorbers 18 from the piezoelectricsubstrate 14 by pressure of water spray, for instance, applied whendicing a wafer can be prevented by making the shape as cornerless aspossible, and making a corner obtuse even when forming a corner asdescribed in each of the above exemplary embodiments.

[0129] (4) A sufficient sound absorbing effect can be obtained by makingthe smallest width portion of the acoustic absorbers 18 in the directionof SAW transmission equal to or greater than 0.5λ (λ=SAW wavelength).

[0130] (5) It is preferable to make the length of the acoustic absorbers18 in the direction orthogonal to the direction of SAW transmissionequal to or greater than the length of the IDT electrodes 15 in the samedirection. This is because, as SAW has a diffraction effect as aproperty of waves, a sufficient sound absorbing effect is obtained bymaking the length equal to or greater than the length of the IDTelectrodes 15 in the same direction.

[0131] (6) In forming the acoustic absorbers 18 having superiorconfigurational accuracy by photolithographic method as in the presentinvention, at least one of the following three methods can be employed.

[0132] The first is a method in which an underlying metal layer 17 isformed on the surface of a wafer in order not to allow light for filmresist exposure from being transmitted to the rear surface of the waferduring the process of forming the acoustic absorbers 18. This method ismost preferable as the underlying metal layer 17 can be formedsimultaneously with the formation of the IDT electrodes 15 andconnection electrodes 16 thus making a separate process unnecessary.

[0133] The second is a method in which rear surface of the wafer isroughened to scatter reflected light so as to avoid impinging ofreflected light from the rear surface of the wafer when exposing filmresist for making acoustic absorbers.

[0134] The third is a method in which an antireflective film 28 isformed on the rear surface of the wafer so as to absorb transmittedlight.

[0135] When forming the underlying metal layer 17 and the antireflectivefilm 28, the size of the antireflective film 28 is made larger than theacoustic absorbers 18 to be formed in order to ensure the above effect.

[0136] (7) In forming the acoustic absorbers 18, when using a filmresist which is equal to or smaller in size than the wafer but largerthan the portion making SAW element 13, or when using a film resistlarger than the wafer, it is preferable to cut it after putting it tothe wafer to a size equal to or smaller than the wafer and larger thanthe portion forming a SAW element 13. The reason is because, if the filmresist is larger than the wafer, there is a possibility that the filmresist may peel off, or smooth transfer may be hindered, by catching onthe transfer device when transferring the wafer for exposure anddevelopment.

[0137] (8) In the second or the fifth exemplary embodiment, a couplingagent is coated over the entire surface of the piezoelectric substrate14. As a result, a coupling layer 21 is formed not only between thepiezoelectric substrate 14 and the acoustic absorbers 18 but also on thesurfaces of the IDT electrodes 15. However, as the coupling layer 21does not do any harm on the characteristics of the SAW device, it is notnecessary to remove it.

[0138] (9) It is preferable to make the bottom surfaces (on the side ofthe piezoelectric substrate 14) larger than the top surfaces of theacoustic absorbers 18 thereby to improve adhesion strength with thepiezoelectric substrate 14.

[0139] (10) Although a silicone resin is used as the filler 25, otherthermosetting resin may also be used. However, it is preferable that thefiller 25 is a material that has higher resilience than that of theacoustic absorbers 18 so that stress applied to the SAW element 13 dueto thermal expansion and the like can be relieved.

[0140] (11) When heating or cooling the piezoelectric substrate 14, itis preferable to avoid abrupt temperature change in order to preventpyroelectric destruction.

[0141] (12) By carrying out anodic oxidation on the surfaces of the IDTelectrodes 15, connection electrodes 16, and underlying metal layers 17and covering their surfaces with an electrically insulating layer,short-circuit between electrodes can be prevented in the event anelectrically conductive foreign object drops on the surface of the SAWelement 13.

INDUSTRIAL APPLICABILITY

[0142] According to the present invention, by forming acoustic absorbershaving the same thickness and main surfaces parallel to the surface of apiezoelectric substrate, mounting failure can be prevented when mountinga SAW element in a package.

1. A surface acoustic wave device comprising: a package having anexternal terminal, a surface acoustic wave element housed in saidpackage, and a lid sealing opening of said package; said surfaceacoustic wave element further comprising on the surface of apiezoelectric substrate: at least an interdigital transducer electrodeand a connection electrode electrically connected to said interdigitaltransducer electrode, and acoustic absorbers formed on both sides ofsaid interdigital transducer electrode, wherein top surfaces of saidacoustic absorbers are parallel to the main surface of saidpiezoelectric substrate and said connection electrode is electricallyconnected to said external terminal.
 2. The surface acoustic wave deviceof claim 1, wherein said acoustic absorbers are formed with aphotosensitive resin.
 3. The surface acoustic wave device of claim 2,wherein said photosensitive resin is negative type.
 4. The surfaceacoustic wave device of claim 2, wherein said photosensitive resin isone selected from the group consisting of epoxy resin, polyimide resin,and acrylic resin.
 5. The surface acoustic wave device of claim 1,wherein the width of said acoustic absorbers in the direction of thetransmission of surface acoustic waves is 0.5λ (λ=wavelength of surfaceacoustic waves) or greater.
 6. The surface acoustic wave device of claim1, wherein the end portion of said acoustic absorbers on the side of theinterdigital transducer electrode is saw-toothed.
 7. The surfaceacoustic wave device of claim 1, wherein a coupling layer havingadhesion strength greater than the adhesion strength between saidacoustic absorbers and said piezoelectric substrate is provided betweensaid acoustic absorbers and said piezoelectric substrate.
 8. The surfaceacoustic wave device of claim 7, wherein said coupling layer has asurface area larger than that of said acoustic absorbers.
 9. The surfaceacoustic wave device of 7, wherein said coupling layer is formed using asilane-based resin.
 10. The surface acoustic wave device of claim 1,wherein an underlying metal layer is provided between said acousticabsorbers and said piezoelectric substrate.
 11. The surface acousticwave device of claim 10, wherein said interdigital transducer electrodeand said underlying metal layer are connected, and said underlying metallayer and said external terminal are connected.
 12. The surface acousticwave device of claim 1, wherein an antireflective film is provided onthe rear surface of said piezoelectric substrate opposite said acousticabsorbers with intervention of said piezoelectric substrate.
 13. Thesurface acoustic wave device of claim 12, wherein the area of formingsaid antireflective film is made larger than said acoustic absorbers.14. The surface acoustic wave device of claim 13, wherein saidantireflective film is formed with amorphous silicon or metal nitridefilm.
 15. The surface acoustic wave device of claim 1, wherein the rearsurface of said piezoelectric substrate is roughened.
 16. The surfaceacoustic wave device of claim 1, wherein the area of the bottom surfaceof said acoustic absorbers that come in contact with said piezoelectricsubstrate is made larger than that of the top surface.
 17. The surfaceacoustic wave device of claim 1, wherein electrical connection betweensaid connection electrode and said external terminal of the package ismade using a bump formed on said connection electrode of said surfaceacoustic wave element.
 18. The surface acoustic wave device of claim 1,wherein said acoustic absorbers are provided on the outer periphery ofsaid piezoelectric substrate in a manner such that they enclose saidinterdigital transducer electrode and said connection electrode.
 19. Thesurface acoustic wave device of claim 18, wherein a filler is providedbetween the inner wall of said package and the side of saidpiezoelectric substrate.
 20. The surface acoustic wave device of claim19, wherein said filler has resilience higher than that of said acousticabsorbers.
 21. The surface acoustic wave device of claim 20, whereinsilicone resin is used as said filler.
 22. The surface acoustic wavedevice of claim 18, wherein acoustic absorbers are provided at least ona region of the rear surface of said piezoelectric substrate oppositesaid interdigital transducer electrode.
 23. The surface acoustic wavedevice of claim 22, wherein said acoustic absorbers provided on the rearsurface of said piezoelectric substrate and a lid are not in contact.24. A method of manufacture of a surface acoustic wave devicecomprising: a first step of forming on a substrate composed of apiezoelectric material at least an interdigital transducer electrode anda connection electrode connected to said interdigital transducerelectrode; a second step of providing a photosensitive resin layer overthe entire surface of said substrate; a third step of forming acousticabsorbers by exposing and developing the portion of said photosensitiveresin which will form acoustic absorbers, and forming a plurality ofsurface acoustic wave elements on said substrate; a fourth step ofplacing in a package a surface acoustic wave element obtained by dicingsaid substrate and electrically connecting said connection electrode ofsaid surface acoustic wave element with an external terminal of saidpackage, and a fifth step of sealing opening of said package with alid;, wherein the main surface of said acoustic absorbers is formedparallel to the surface of said substrate.
 25. The method of manufactureof a surface acoustic wave device of claim 24, wherein saidphotosensitive resin layer is formed using a film resist.
 26. The methodof manufacture of a surface acoustic wave device of claim 24, whereinthe thickness of said photosensitive resin layer in the second step isequal to or less than that of the substrate composed of a piezoelectricmaterial and is greater than the thickness of the portion where asurface acoustic wave element is formed.
 27. The method of manufactureof a surface acoustic wave device of claim 24, wherein an underlyingmetal layer is formed in the first step together with an interdigitaltransducer electrode at the location where acoustic absorbers are to beformed.
 28. The method of manufacture of a surface acoustic wave deviceof claim 24, wherein a protective layer is provided on the surface ofsaid interdigital transducer electrode after the first step and prior tothe second step.
 29. The method of manufacture of a surface acousticwave device of claim 28, wherein said protective layer is formed byanodic oxidation.
 30. The method of manufacture of a surface acousticwave device of claim 24, wherein a metal film is formed on the surfaceof said substrate composed of a piezoelectric material prior to thefirst step and an electrically insulating layer is formed on the surfaceof said metal film by anodic oxidation.
 31. The method of manufacture ofa surface acoustic wave device of claim 24, wherein a silane-basedcoupling layer is formed after the first step and prior to the secondstep at the location on said substrate composed of a piezoelectricmaterial where acoustic absorbers are to be formed.
 32. The method ofmanufacture of a surface acoustic wave device of claim 24, wherein anantireflective film is provided prior to the first step in a region onthe rear surface of said substrate composed of a piezoelectric materialopposite the location with intervention of said piezoelectric substratewith intervention of said piezoelectric substrate where acousticabsorbers are to be formed.
 33. The method of manufacture of a surfaceacoustic wave device of claim 24, wherein a step of roughening the rearsurface of said substrate composed of a piezoelectric material isincluded prior to the first step.